1. Field of the Invention
The present invention relates to surgical methods and devices to treat back and leg pain and in particular to the surgical insertion of prosthetic nucleus replacement within the annulus fibrosis. The device replaces a portion of a damaged spinal intervertebral disc to restore function.
2. Description of Related Art
In the spine, the principal function of the disco-vertebral joint is to transmit compressive loads and still allow flexibility. Adjacent vertebrae are joined by a triple-joint complex. The anterior complex or column is formed by the vertebral bodies which are shaped like flattened cylinders with discoid shaped or ovoid shaped intervertebral discs sandwiched between each vertebral body. Facet joints in the rear of each vertebra have a smooth cartilage surface, lubricating joint fluid, and a covering capsule. The facet joints restrict the disc to small degrees of flexion and extension, limit rotation, and protect against translational shear stress. The disc itself comprises two principle parts, the nucleus pulposus at the core, and the annulus fibrosis, which is a multilayer bias-ply wrapping that surrounds the nucleus. The nucleus starts early in life as eighty percent water, and slowly desiccates with age.
A damaged disc can cause nerve dysfunction and debilitating pain in the back, legs and arms. Typical treatments that provide relief and allow patients to function again include back braces, medical treatment, physical therapy and surgery to remove the disc. A conventional surgical solution removes the bad disc and promotes new bone growth in the space to fuse the adjacent vertebrae together.
Several different prosthetic intervertebral disc devices are described by Casey K. Lee, et al., in "Prosthetic Intervertebral Disc," Chapter 96, The Adult Spine: Principles and Practice, Raven Press, Ltd., New York, .COPYRGT. 1991. The conclusion of Lee, et al., is that "An appropriately designed and fabricated prosthetic intervertebral disc may provide an improved alternative to currently available surgical approaches to low back disorders." Lee, et al., describe their work at the orthopedic research laboratories at the New Jersey Medical School "to produce a prosthetic intervertebral disc design that has biomechanical characteristics similar to the natural disc." One result has been the manufacture of a unit with a nucleus, annulus, and end plates that are molded under heat and fused into a single prosthetic disc. However, success of such a device depends on solid bone attachment. Most prior concepts have been excessively complex and never used.
A prosthetic nucleus replacement can be surgically implanted within the annulus fibrosis. The natural attachments of the annulus would therefore be able to produce the requisite tensile strength of the repaired site. The prosthetic nucleus replacement would be subject primarily to compressive forces.